Non-aqueous pigment dispersions using dispersion synergists

ABSTRACT

A non-aqueous pigment dispersion includes a diketopyrrolo-pyrrole pigment, a polymeric dispersant, and a dispersion synergist in a dispersion medium wherein the dispersion synergist is a quinacridone derivative containing at least one acid group or a salt thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2006/069014, filed Nov. 28, 2006. This application claims thebenefit of U.S. Provisional Application No. 60/750,577, filed Dec. 15,2005, which is incorporated by reference herein in its entirety. Inaddition, this application claims the benefit of European ApplicationNo. 05111358.7, filed Nov. 28, 2005, which is also incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to stable diketopyrrolo-pyrroledispersions and inkjet inks using specific dispersion synergists.

2. Description of the Related Art

Pigment dispersions are made using a dispersant. A dispersant is asubstance for promoting the formation and stabilization of a dispersionof pigment particles in a dispersion medium. Dispersants are generallysurface-active materials having an anionic, cationic or non-ionicstructure. The presence of a dispersant substantially reduces therequired dispersing energy. Dispersed pigment particles may have atendency to re-agglomerate after the dispersing operation due to mutualattraction forces. The use of dispersants also counteracts thisre-agglomeration tendency of the pigment particles.

The dispersant has to meet particularly high requirements when used forinkjet inks. Inadequate dispersing manifests itself as increasedviscosity in liquid systems, loss of brilliance and/or hue shifts.Moreover, particularly good dispersion of the pigment particles isrequired to ensure unimpeded passage of the pigment particles throughthe nozzles of the print head, which are usually only a few micrometersin diameter. In addition, pigment particle agglomeration and theassociated blockage of the printer nozzles has to be avoided during thestandby periods of the printer.

Polymeric dispersants contain in one part of the molecule so-calledanchor groups, which adsorb onto the pigments to be dispersed. In aspatially separate part of the molecule, polymeric dispersants havepolymer chains compatible with the dispersion medium, thus stabilizingthe pigment particles in the dispersion medium. Typical polymericdispersants include graft copolymer and block copolymer dispersants.

In aqueous inkjet inks, the polymeric dispersants generally containhydrophobic anchor groups exhibiting a high affinity for the pigmentsurface and hydrophilic polymer chains for stabilizing the pigments inthe aqueous dispersion medium.

The preparation of good thermally stable dispersions with submicronparticles is more difficult for non-aqueous inkjet inks, such as solventbased, oil based and radiation curable inkjet inks. The pigments areespecially difficult to disperse when they have a non-polar surface.

These problems have led to the design of very specific polymericdispersants wherein the anchor groups are pigment derivatives. Forexample, EP 0763378 A (TOYO INK) discloses a pigment compositionincluding a non-aqueous type pigment dispersing agent having a portionwhich has a high affinity with a pigment and which has at least one typeselected from the group consisting of an organic dye, anthraquinone andacridone only at a terminal end or at both terminal ends of at least onepolymer selected from a linear urethane polymer and a linear acrylicpolymer, and a pigment.

Another approach for dispersing pigments with non-polar surfaces innon-aqueous dispersion media is changing the surface to a more polarsurface by addition of compounds known as dispersion synergists. Adispersion synergist is a compound that promotes the adsorption of thepolymeric dispersant on the surface of the pigment. It is suggested thatthe synergist should possess the pigment structure substitued by one ormore sulphonic acid groups or ammonium salts thereof.

U.S. Pat. No. 4,461,647 (ICI) discloses a dispersion of a pigment in anorganic liquid containing a water-insoluble asymmetric disazo compoundincluding a central divalent group free from acidic and other ionicsubstituents linked through azo groups to two monovalent end groupswherein one end group, the first, is free from acidic and other ionicsubstituents and the other end group, the second, carries a singlesubstituted ammonium-acid salt group.

U.S. Pat. No. 4,057,436 (ICI) discloses pigment dispersions in organicliquids using polymeric or resinous dispersing agents in the presence ofa substituted ammonium salt of a colored acid wherein there are between16 and 60 carbon atoms contained in at least 3 chains attached to theN-atom of the substituted ammonium ion.

U.S. Pat. No. 6,641,655 (AVECIA) discloses the use of a diquaternaryammonium salt of a colored acid as a fluidizing agent wherein thediquaternary ammonium cation contains two or more nitrogen atoms.

Although these dispersion synergists work fine for some pigments, manyother pigments cannot be dispersed to an acceptable quality in anon-aqueous medium. This is the case for diketopyrrolo-pyrrole pigments,for which it is difficult to obtain stable non-aqueous pigmentdispersions, especially stable non-aqueous ink-jet inks.

U.S. Pat. No. 6,821,334 (DAINICHISEIKA COLOR) discloses a surfacemodification of the diketopyrrolo-pyrrole pigments C.I. Pigment Red 254and C.I. Pigment Red 255. The sulfonated particles are easilydispersible as an aqueous pigment dispersion, but no details are givenon their performance in non-aqueous pigment dispersions.

U.S. 2004/0122130 (CHANG ET AL.) discloses a photocurable pigment typeinkjet ink composition containing Pigment Red 254 but the ink requiresthe presence of water and a reactive surfactant.

EP 224445 A (CIBA) discloses pigment dispersions of pyrrolo-pyrrolepigments with dispersion synergists including sulphonic acid groups,carboxyl groups, phosphate groups and salts thereof on the phenyl ringof the pyrrolo-pyrrole pigment of which it is derived.

JP 2004-067714 (TORAY INDUSTRIES) discloses pigment dispersionsincluding dispersion synergists including sulphonic acid groups,carboxyl groups and salts thereof on the phenyl ring of thepyrrolo-pyrrole pigment of which it is derived.

JP 2003-346926 (TOYO INK) discloses a sensitizing dye for photoelectricconversion used in a dye sensitized photoelectric converting cellwherein the sensitizing dye is a diketopyrrolopyrrole compoundsubstituted on both nitrogen atoms with a monovalent organic residue.

For consistent image quality, inkjet inks require a dispersion stabilitycapable of dealing with high temperatures (above 60° C.) duringtransport of the ink to a customer, jetting at elevated temperatures andchanges in the dispersion medium of the inkjet ink during use, forexample, evaporation of solvent and increasing concentrations ofhumectants, penetrants and other additives.

Therefore, it is highly desirable to manufacture pigmented inkjet inksusing diketopyrrolo-pyrrole pigments in a non-aqueous medium exhibitinga high dispersion quality and stability.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide non-aqueous diketopyrrolo-pyrrolepigment dispersions with high dispersion quality and stability.

Further preferred embodiments of the present invention providenon-aqueous diketopyrrolo-pyrrole inkjet inks producing images of highimage quality with a high optical density.

Further advantages of the present invention will become apparent fromthe description hereinafter.

It has been surprisingly discovered that non-aqueousdiketopyrrolo-pyrrole pigment dispersions of high dispersion quality andstability were obtained by using a quinacridone derivative containing acarboxyl group.

Advantages of the present invention have been achieved with anon-aqueous pigment dispersion including a diketopyrrolo-pyrrolepigment, a polymeric dispersant and a dispersion synergist in adispersion medium wherein the dispersion synergist is a quinacridonederivative containing at least one acid group or a salt thereof.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Definitions

The term “colorant”, as used in the preferred embodiments of the presentinvention means dyes and pigments.

The term “dye”, as used in the preferred embodiments of the presentinvention means a colorant having a solubility of 10 mg/L or more in themedium in which it is applied and under the ambient conditionspertaining.

The term “pigment” is defined in DIN 55943, herein incorporated byreference, as a coloring agent that is practically insoluble in theapplication medium under the pertaining ambient conditions, hence havinga solubility of less than 10 mg/L therein.

The term “C.I.” is used in the preferred embodiments of the presentapplication as an abbreviation for Colour Index.

The term “actinic radiation” as used in the preferred embodiments of thepresent invention, means electromagnetic radiation capable of initiatingphotochemical reactions.

The term “spectral separation factor” as used in the preferredembodiments of the present invention means the value obtained bycalculating the ratio of the maximum absorbance A_(max) (measured atwavelength λ_(max)) over the reference absorbance A_(ref) determined ata higher wavelength λ_(ref).

The abbreviation “SSF” is used in the preferred embodiments of thepresent invention for spectral separation factor.

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group, i.e., for three carbon atoms: n-propyl andisopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl;for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyland 2-methyl-butyl etc.

The term “carboxyl group” as used in the preferred embodiments of thepresent invention means the functional group of carboxylic acid, i.e.,—COOH. It is also known as carboxy group.

Pigment Dispersions

The non-aqueous pigmented dispersion according to a preferred embodimentof the present invention contains at least three components: (i) adiketopyrrolo-pyrrole pigment, (ii) a polymeric dispersant and (iii) adispersion synergist. The components are preferably present in anon-aqueous liquid dispersion medium.

The term “non-aqueous liquid” refers to a liquid carrier which shouldcontain no water. However, sometimes a small amount, generally less than5 wt % of water based on the total weight of the pigmented dispersion,can be present. This water is not intentionally added but comes into theformulation via other components as a contamination, such as for examplepolar organic solvents. Higher amounts of water than 5 wt % tend to makethe non-aqueous pigmented dispersions unstable, preferably the watercontent is less than 1 wt % based on the total weight dispersion mediumand most preferably no water at all is present.

The non-aqueous pigmented dispersion according to a preferred embodimentof the present invention may further also contain at least onesurfactant.

In a preferred embodiment, the non-aqueous pigmented dispersion is anon-aqueous inkjet ink. The non-aqueous inkjet ink may contain at leastone humectant to prevent the clogging of the nozzle, due to its abilityto slow down the evaporation rate of ink.

The non-aqueous inkjet ink is preferably an inkjet ink selected from thegroup consisting of an organic solvent based, an oil based and a curableinkjet ink. The curable inkjet ink is preferably radiation curable.

The viscosity of the inkjet ink is preferably lower than 100 mPa·s at30° C. The viscosity of the inkjet ink is preferably lower than 30mPa·s, more preferably lower than 15 mPa·s, and most preferably between2 and 10 mPa·s at a shear rate of 100 s⁻¹ and a jetting temperaturebetween 10 and 70° C.

The curable inkjet ink may contain as a dispersion medium monomers,oligomers and/or prepolymers possessing different degrees offunctionality. A mixture including combinations of mono-, di-, tri-and/or higher functionality monomers, oligomers or prepolymers may beused. A catalyst called an initiator for initiating the polymerizationreaction may be included in the curable inkjet ink. The initiator can bea thermal initiator, but is preferably a photo-initiator. Thephoto-initiator requires less energy to activate than the monomers,oligomers and/or prepolymers to form the polymer. The photo-initiatorsuitable for use in the curable pigment dispersion may be a Norrish typeI initiator, a Norrish type II initiator or a photo-acid generator.

The non-aqueous inkjet ink is particularly suitable as a magenta inkjetink in a non-aqueous CMYK inkjet ink set. The non-aqueous CMYK inkjetink set may also be extended with extra inks such as red, green, blue,and/or orange to further enlarge the color gamut of the image. The CMYKink set may also be extended by the combination of full density andlight density inks of both color inks and/or black inks to improve theimage quality by lowered graininess.

Dispersion Synergists

The non-aqueous pigment dispersion according to a preferred embodimentof the present invention contains at least one quinacridone derivativecontaining at least one acid group or a salt thereof as a dispersionsynergist. A mixture of dispersion synergists may be used to obtainbetter dispersion stability.

The dispersion synergist is preferably a quinacridone derivativesubstituted on only one of the two nitrogen atoms of the quinacridonebasic chromophore structure with at least one acid group or a saltthereof. The pigment C.I. Pigment Violet 19 represents the quinacridonebasic chromophore structure.

The at least one acid group or a salt thereof may be an alkanoic acidgroup, an alicyclic acid group, a heterocyclic acid group, ahetero-aromatic acid group, an aromatic acid group or salts thereof.

The aromatic acid group or a salt thereof is preferably a benzoic acidgroup or a salt therof.

The dispersion synergist may contain two or more acid groups, preferablyin meta- or para-position on a phenyl ring. A preferred aromatic acidgroup or a salt thereof containing two carboxyl groups or salts thereofis a phthalic acid group or a salt thereof. Preferably, the phthalicacid group is an isophthalic group.

A combination of different types of acid groups may also beadvantageously used. For example, a combination of a carboxyl group anda sulphonic acid, a phosphoric acid or a phenolic group can also beadvantageously used.

The at least one acid group or a salt thereof may be attached directlyto the quinacridone structure or may be attached through a linking groupcontaining 1 or more carbon atoms. The linking group contains preferably1 to 20 carbon atoms, more preferably 1 to 12 and most preferably 1 to 6carbon atoms. In a preferred embodiment, the linking group is a straightchain of 1 or more carbon atoms, wherein some of the carbon atoms may besubstituted by a heteroatom such as an oxygen atom, a nitrogen atom, asulphur atom, a phosphorous atom, selenium atom and a tellurium atom. Itis also possible that, if present, some of the hydrogen atoms attachedto a carbon atom are substituted by a heteroatom such as an oxygen atom,a nitrogen atom, a sulphur atom, a halogen atom, a phosphorous atom,selenium atom and a tellurium atom.

The dispersion synergist is preferably a quinacridone derivativeaccording to formula (A):

wherein R¹ and R² are each independently selected from the groupconsisting of hydrogen, methyl, ethyl and halogen; and R³ represents theat least one acid group.

In a preferred embodiment, the dispersion synergist is a quinacridonederivative represented by Formula (I):

wherein R¹ and R² are each independently selected from the groupconsisting of hydrogen, methyl, ethyl and halogen.

In a more preferred embodiment, the quinacridone derivative isrepresented by Formula (II):

wherein R¹ and R² are each independently selected from the groupconsisting of hydrogen, methyl, ethyl and halogen.

The most preferred quinacridone derivative is:

Another preferred quinacridone derivative is the quinacridone derivativeaccording to Formula (II) wherein R¹ and R² are both hydrogen.

Another preferred quinacridone derivative is the quinacridone derivativeaccording to Formula (II) wherein R¹ and R² are both a methyl group.

A mixture of the quinacridone derivatives according to Formula (I) andone or more other dispersion synergists may also be used to obtainbetter dispersion quality and stability.

In case that the dispersion synergist contains a salt of an acid group,the charge of the anion is compensated by a cation.

The cation may be an inorganic cation selected from the group consistingof the Ia and IIa metals in the table of Mendeleev. In a preferredembodiment, the cation is Li⁺.

The cation is preferably an organic cation. A preferred cation is anammonium and a substituted ammonium group. In a preferred embodiment,the cation is selected from the substituted ammonium cations disclosedin U.S. Pat. No. 4,461,647 (ICI), U.S. Pat. No. 4,057,436 (ICI) and U.S.Pat. No. 6,641,655 (AVECIA) all incorporated herein by reference.

Particularly preferred cations include the substituted ammonium groupsselected from the group consisting of ⁺N(CH₃)₂(C₁₈H₃₇)₂,⁺NH(CH₃)₂(C₁₈H₃₇), ⁺N(CH₃)₂(C₁₂H₂₅)₂, ⁺NH(CH₃)₂(C₁₂H₂₅), ⁺N(CH₃)₂,(C₁₀H₂₁)₂, ⁺NH(CH₃)₂(C₁₀H₂₁), ⁺N(CH₃)₂(C₈H₁₇)₂, ⁺NH(CH₃)₂(C₈H₁₇),⁺NH(C₈H₁₇)₃, ⁺NH(C₁₀H₂₁)₃, ⁺NH(C₁₂H₂₅)₃ and ⁺NH(C₁₈H₃₅)₃.

In a preferred embodiment, the at least one acid group is a carboxylgroup. Suitable dispersion synergists include those disclosed in Table1.

TABLE 1 Dis- persion Syner- gist Chemical Structure QAD-1

QAD-2

QAD-3

QAD-4

QAD-5

QAD-6

QAD-7

QAD-8

QAD-9

QAD- 10

QAD- 11

QAD- 12

QAD- 13

QAD- 14

QAD- 15

QAD- 16

QAD- 17

The subsituted ammonium group can also be chemically represented as anamine with the hydrogen attached to the carboxylate anion. This isexemplified for the structures QAD-6, QAD-7, QAD-8, QAD-11, QAD-12 andQAD-15 to QAD-17 of Table 1.

The dispersion synergist is preferably added in an amount between 0.1and 20 wt % based upon the weight of the pigment.

The synergist should be additional to the amount of polymericdispersant(s). The ratio of polymeric dispersant/dispersion synergistdepends upon the pigment and should be determined experimentally.Typically the ratio wt % polymeric dispersant/wt % dispersion synergistis selected between 2:1 to 100:1, preferably between 2:1 and 20:1.

Diketopyrrolo-pyrrole Pigments

The color pigment in the non-aqueous pigment dispersion according to apreferred embodiment of the present invention is a diketopyrrolo-pyrrolepigment. Preferably, the diketopyrrolo-pyrrole pigment is represented byFormula (I):

wherein R1 and R2 are independently selected from the group consistingof hydrogen, a halogen atom, a methyl group, an ethyl group, antert.-butyl group, a phenyl group and a cyano group.

Particularly preferred diketopyrrolo-pyrrole pigments are C.I. PigmentOrange 71, C.I. Pigment Orange 73, C.I. Pigment Orange 81, C.I. PigmentRed 254, C.I. Pigment Red 255, C.I. Pigment Red 264, C.I. Pigment Red270, C.I. Pigment Red 272 or mixed crystals thereof.

Suitable diketopyrrolo-pyrrole pigments include mixed crystals of adiketopyrrolo-pyrrole pigment and a quinacridone pigment. Thequinacridone pigment may be chosen from those disclosed by HERBST,Willy, et al., Industrial Organic Pigments, Production, Properties,Applications, 3rd Edition, Wiley-VCH, 2004, ISBN 3527305769. Suitableexamples of mixed crystals of a diketopyrrolo-pyrrole pigment and aquinacridone pigment are disclosed in EP 0277914 A (CIBA), U.S. Pat. No.4,810,304 (CIBA), EP 0704496 A (CIBA), EP 0765919 A (CIBA) and EP0794235 A (CIBA).

Pigment particles in pigmented inkjet ink should be sufficiently smallto permit free flow of the ink through the inkjet-printing device,especially at the ejecting nozzles. It is also desirable to use smallparticles for maximum color strength and to slow down sedimentation.

The average particle size of the pigment in a pigmented inkjet inkshould be between 0.005 and 15 μm. Preferably, the numeric averagepigment particle size is between 0.005 and 5 μm, more preferably between0.005 and 1 μm, particularly preferably between 0.005 and 0.3 μm andmost preferably between 0.040 and 0.150 μm.

The diketopyrrolo-pyrrole pigment is preferably used in the non-aqueouspigment dispersion in an amount of 0.1 to 20 wt %, preferably 1 to 10 wt% based on the total weight of the non-aqueous pigment dispersion.

Dispersants

Typical polymeric dispersants are copolymers of two monomers but maycontain three, four, five or even more monomers. The properties ofpolymeric dispersants depend on both the nature of the monomers andtheir distribution in the polymer. Suitable copolymeric dispersants havethe following polymer compositions:

-   -   statistically polymerized monomers (e.g., monomers A and B        polymerized into ABBAABAB);    -   alternating polymerized monomers (e.g., monomers A and B        polymerized into ABABABAB);    -   gradient (tapered) polymerized monomers (e.g., monomers A and B        polymerized into AAABAABBABBB);    -   block copolymers (e.g., monomers A and B polymerized into        AAAAABBBBBB) wherein the block length of each of the blocks (2,        3, 4, 5 or even more) is important for the dispersion capability        of the polymeric dispersant;    -   graft copolymers (graft copolymers consist of a polymeric        backbone with side chains attached to the backbone); and    -   mixed forms of these polymers, e.g., blocky gradient copolymers.

Polymeric dispersants may have different polymer architectures includinglinear, comb/branched, star, dendritic (including dendrimers andhyperbranched polymers). A general review on the architecture ofpolymers is given by ODIAN, George, Principles Of Polymerization, 4thEdition, Wiley-Interscience, 2004, pp. 1-18.

Comb/branched polymers have side branches of linked monomer moleculesprotruding from various central branch points along the main polymerchain (at least 3 branch points).

Star polymers are branched polymers in which three or more eithersimilar or different linear homopolymers or copolymers are linkedtogether to a single core.

Dendritic polymers include the classes of dendrimers and hyperbranchedpolymers. In dendrimers, with well-defined mono-disperse structures, allbranch points are used (multi-step synthesis), while hyperbranchedpolymers have a plurality of branch points and multifunctional branchesthat lead to further branching with polymer growth (one-steppolymerization process).

Suitable polymeric dispersants may be prepared via addition orcondensation type polymerizations. Polymerization methods include thosedescribed by ODIAN, George, Principles Of Polymerization, 4th Edition,Wiley-Interscience, 2004, pp. 39-606.

Addition polymerization methods include free radical polymerization(FRP) and controlled polymerization techniques. Suitable controlledradical polymerization methods include:

-   -   RAFT: reversible addition-fragmentation chain transfer;    -   ATRP: atom transfer radical polymerization    -   MADIX: reversible addition-fragmentation chain transfer process,        using a transfer active xanthate;    -   Catalytic chain transfer (e.g., using cobalt complexes); and    -   Nitroxide (e.g., TEMPO) mediated polymerizations;

Other suitable controlled polymerization methods include:

-   -   GTP: group transfer polymerization;    -   Living cationic (ring-opening) polymerizations;    -   Anionic co-ordination insertion ring-opening polymerization; and    -   Living anionic (ring-opening) polymerization.

Reversible addition-fragmentation transfer (RAFT): controlledpolymerization occurs via rapid chain transfer between growing polymerradicals and dormant polymer chains. A review article on RAFT synthesisof dispersants with different polymeric geometry is given in QUINN J. F.et al., Facile Synthesis of Comb, Star, and Graft Polymers ViaReversible Addition-fragmentation Chain Transfer (RAFT) Polymerization,Journal of Polymer Science, Part A: Polymer Chemistry, Vol. 40, pp.2956-2966, 2002.

Group transfer polymerization (GTP): the method of GTP used forsynthesis of AB block copolymers is disclosed by SPINELLI, Harry J., GTPand Its Use in Water Based Pigment Dispersants and Emulsion Stabilisers,Proc. of 20th Int.. Conf. Org. Coat. Sci. Technol., New Platz, N.Y.,State Univ. N.Y., Inst. Mater. Sci., pp. 511-518.

The synthesis of dendritic polymers is described in the literature. Thesynthesis of dendrimers in NEWCOME, G. R., et al. Dendritic Molecules:Concepts, Synthesis, Perspectives, VCH: WEINHEIM, 2001. Hyperbranchingpolymerization is described by BURCHARD, W., Solution Properties ofBranched Macromolecules, Advances in Polymer Science, 1999, Vol. 143,No. II, pp. 113-194. Hyperbranched materials can be obtained bypolyfunctional polycondensation as disclosed by FLORY, P. J., MolecularSize Distribution in Three-dimensional Polymers, VI. Branched PolymerContaining A-R-Bf-1-type Units, Journal of the American ChemicalSociety, 1952, Vol. 74, pp. 2718-2723.

Living cationic polymerizations is, e.g., used for the synthesis ofpolyvinyl ethers as disclosed in WO 2005/012444 (CANON), U.S.2005/0197424 (CANON) and U.S. 2005/0176846 (CANON). Anionicco-ordination ring-opening polymerization is, e.g., used for thesynthesis of polyesters based on lactones. Living anionic ring-openingpolymerization is, e.g., used for the synthesis of polyethylene oxidemacromonomers.

Free radical Polymerization (FRP) proceeds via a chain mechanism, whichbasically includes four different types of reactions involving freeradicals: (1) radical generation from non-radical species (initiation),(2) radical addition to a substituted alkene (propagation), (3) atomtransfer and atom abstraction reactions (chain transfer and terminationby disproportionation), and (4) radical-radical recombination reactions(termination by combination).

Polymeric dispersants having several of the above polymer compositionsare disclosed in U.S. Pat. No. 6,022,908 (HP), U.S. Pat. No. 5,302,197(DU PONT) and U.S. Pat. No. 6,528,557 (XEROX).

Suitable statistical copolymeric dispersants are disclosed in U.S. Pat.No. 5,648,405 (DU PONT), U.S. Pat. No. 6,245,832 (FUJI XEROX), U.S. Pat.No. 6,262,207 (3M), U.S. Pat. No. 2005/0004262 (KAO) and U.S. Pat. No.6,852,777 (KAO).

Suitable alternating copolymeric dispersants are described in U.S.2003/0017271 (AKZO NOBEL).

Suitable block copolymeric dispersants have been described in numerouspatents, especially block copolymeric dispersants containing hydrophobicand hydrophilic blocks. For example, U.S. Pat. No. 5,859,113 (DU PONT)AB block copolymers, U.S. Pat. No. 6,413,306 (DU PONT) discloses ABCblock copolymers.

Suitable graft copolymeric dispersants are described in CA 2157361 (DUPONT) (hydrophobic polymeric backbone and hydrophilic side chains);other graft copolymeric dispersants are disclosed in U.S. Pat. No.6,652,634 (LEXMARK) and U.S. Pat. NO. 6,521,715 (DU PONT).

Suitable branched copolymeric dispersants are described U.S. Pat. No.6,005,023 (DU PONT), U.S. Pat. No. 6,031,019 (KAO), and U.S. Pat. No.6,127,453 (KODAK).

Suitable dendritic copolymeric dispersants are described in, e.g., U.S.Pat. No. 6,518,370 (3M), U.S. Pat. No. 6,258,896 (3M), WO 00/063305 (GEMGRAVURE), U.S. Pat. No. 6,649,138 (QUANTUM DOT), U.S. Pat. No.2002/0256230 (BASF), EP 1351759 A (EFKA ADDITIVES) and EP 1295919 A(KODAK).

Suitable designs of polymeric dispersants for inkjet inks are disclosedin SPINELLI, Harry J., Polymeric Dispersants in Inkjet technology,Advanced Materials, 1998, Vol. 10, No. 15, pp. 1215-1218.

The monomers and/or oligomers used to prepare the polymeric dispersantcan be any monomer and/or oligomer found in the Polymer Handbook Vol.1+2, 4th Edition, edited by J. BRANDRUP et al., Wiley-Interscience,1999.

Polymers useful as pigment dispersants include naturally occurringpolymers, and specific examples thereof include: proteins, such as glue,gelatine, casein, and albumin; naturally occurring rubbers, such as gumarabic and tragacanth; glucosides such as saponin; alginic acid andalginic acid derivatives, such as propylene glycol alginate; andcellulose derivatives, such as methyl cellulose, carboxymethyl celluloseand ethylhydroxy cellulose; wool and silk, and synthetic polymers.

Suitable examples of monomers for synthesising polymeric dispersantsinclude: acrylic acid, methacrylic acid, maleic acid (or there salts),maleic anhydride, alkyl(meth)acrylates (linear, branched and cycloalkyl)such as methyl(meth)acrylate, n-butyl(meth)acrylate,tert-butyl(meth)acrylate, cyclohexyl(meth)acrylate, and2-ethylhexyl(meth)acrylate; aryl(meth)acrylates such asbenzyl(meth)acrylate, and phenyl(meth)acrylate;hydroxyalkyl(meth)acrylates such as hydroxyethyl(meth)acrylate, andhydroxypropyl(meth)acrylate; (meth)acrylates with other types offunctionalities (e.g., oxiranes, amino, fluoro, polyethylene oxide,phosphate substituted) such as glycidyl (meth)acrylate,dimethylaminoethyl(meth)acrylate, trifluoroethyl acrylate,methoxypolyethyleneglycol (meth)acrylate, and tripropyleneglycol(meth)acrylate phosphate; allyl derivatives such as allyl glycidylether; styrenics such as styrene, 4-methylstyrene, 4-hydroxystyrene,4-acetostyrene, and styrene sulfonic acid; (meth)acrylonitrile;(meth)acrylamides (including N-mono and N,N-disubstituted) such asN-benzyl (meth)acrylamide; maleimides such as N-phenyl maleimide; vinylderivatives such as vinyl alcohol, vinylcaprolactam, vinylpyrrolidone,vinylimidazole, vinylnapthalene, and vinyl halides; vinylethers such asvinylmethyl ether; vinylesters of carboxylic acids such as vinylacetate,vinylbutyrate, and vinyl benzoate. Typical condensation type polymersinclude polyurethanes, polyamides, polycarbonates, polyethers,polyureas, polyimines, polyimides, polyketones, polyester, polysiloxane,phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde,polysulfide, polyacetal or combinations thereof.

Suitable copolymeric dispersants are acrylic acid/acrylonitrilecopolymer, vinyl acetate/acrylic ester copolymer, acrylic acid/acrylicester copolymer, styrene/acrylic acid copolymer, styrene/methacrylicacid copolymer, styrene/methacrylic acid/acrylic ester copolymer,styrene/α-methylstyrene/acrylic acid copolymer,styrene/α-methylstyrene/acrylic acid/acrylic ester copolymer,styrene/maleic acid copolymer, styrene/maleic anhydride copolymer,vinylnaphthalene/acrylic acid copolymer, vinylnapthalene/maleic acidcopolymer, vinyl acetate/ethylene copolymer, vinyl acetate/fattyacid/ethylene copolymer, vinyl acetate/maleic ester copolymer, vinylacetate/crotonic acid copolymer, vinyl acetate/acrylic acid copolymer.

Suitable chemistries of copolymeric dispersants also include:

-   -   Copolymers which are the product of a condensation process of        poly(ethylene imine) with a carboxylic acid terminated polyester        (made by addition polymerization); and    -   Copolymers which are the product of a reaction of a        multifunctional isocyanate with:        -   a compound monosubstituted with a group that is capable of            reacting with an isocyanate, e.g., polyester;        -   a compound containing two groups capable of reacting with an            isocyanate (cross-linker); or        -   a compound with at least one basic ring nitrogen and a group            that is capable of reacting with an isocyanate group.

A detailed list of suitable polymeric dispersants is disclosed by MCCUTCHEON, Functional Materials, North American Edition, Glen Rock, N.J.:Manufacturing Confectioner Publishing Co., 1990, pp. 110-129.

Suitable pigment stabilizers are also disclosed in DE 19636382 (BAYER),U.S. Pat. No. 5,720,802 (XEROX), U.S. Pat. No. 5,713,993 (DU PONT), WO96/12772 (XAAR), and U.S. Pat. No. 5,085,689 (BASF).

One polymeric dispersant or a mixture of two or more polymericdispersants may be present to improve the dispersion stability further.Sometimes surfactants can also be used as pigment dispersants, thus acombination of a polymeric dispersant with a surfactant is alsopossible.

The polymeric dispersant can be non-ionic, anionic or cationic innature; salts of the ionic dispersants can also be used.

The polymeric dispersant preferably has a polymerization degree DPbetween 5 and 1,000, more preferably between 10 and 500 and mostpreferably between 10 and 100.

The polymeric dispersant preferably has a number average molecularweight Mn between 500 and 30,000, more preferably between 1,500 and10,000.

The polymeric dispersant preferably has an average molecular weight Mwsmaller than 100,000, more preferably smaller than 50,000 and mostpreferably smaller than 30,000.

The polymeric dispersant preferably has a polymeric dispersity PDsmaller than 2, more preferably smaller than 1.75 and most preferablysmaller than 1.5.

Commercial examples of polymeric dispersants are the following:

-   -   DISPERBYK™ dispersants available from BYK CHEMIE GMBH;    -   SOLSPERSE™ dispersants available from NOVEON;    -   TEGO™ DISPERS™ dispersants from DEGUSSA;    -   EDAPLAN™ dispersants from MÜNNZING CHEMIE;    -   ETHACRYL™ dispersants from LYONDELL;    -   GANEX™ dispersants from ISP;    -   DISPEX™ and EFKA™ dispersants from CIBA SPECIALTY CHEMICALS INC;    -   DISPONER™ dispersants from DEUCHEM; and    -   JONCRYL™ dispersants from JOHNSON POLYMER.

Particularly preferred polymeric dispersants include Solsperse™dispersants from NOVEON, Efka™ dispersants from CIBA SPECIALTY CHEMICALSINC and Disperbyk™ dispersants from BYK CHEMIE GMBH.

Particularly preferred dispersants for solvent based pigmenteddispersions are Solsperse™ 32000 and 39000 from NOVEON.

Particularly preferred dispersants for oil based pigmented dispersionsare Solsperse™ 11000, 11200, 13940, 16000, 17000 and 19000 from NOVEON.

Particularly preferred dispersants for UV-curable pigmented dispersionsare Solsperse™ 32000 and 39000 dispersants from NOVEON.

The polymeric dispersant is preferably used in an amount of 2 to 600 wt%, more preferably 5 to 200 wt % based on the weight of the pigment.

Dispersion Media

In one preferred embodiment, the dispersion medium includes organicsolvent(s). Suitable organic solvents include alcohols, ketones, esters,ethers, glycols and polyglycols and derivatives thereof, lactones,N-containing solvents such as amides. Preferably mixtures of one or moreof these solvents are used.

Examples of suitable alcohols include methyl alcohol, ethyl alcohol,n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, heptyl alcohol,octyl alcohol, cyclohexyl alcohol, benzyl alcohol, phenylethyl alcohol,phenylpropyl alcohol, furfuryl alcohol, anise alcohol andfluoroalcohols.

Examples of suitable ketones include acetone, methyl ethyl ketone,methyl n-propyl ketone, methyl isopropyl ketone, methyl n-butyl ketone,methyl isobutyl ketone, methyl n-amyl ketone, methyl isoamyl ketone,diethyl ketone, ethyl n-propyl ketone, ethyl isopropyl ketone, ethyln-butyl ketone, ethyl isobutyl ketone, di-n-propyl ketone, diisobutylketone, cyclohexanone, methylcyclohexanone and isophorone,2,4-pentanedione and hexafluoroacetone.

Examples of suitable esters include methyl acetate, ethyl acetate,n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate,hexyl acetate, octyl acetate, benzyl acetate, phenoxyethyl acetate,ethyl phenyl acetate, methyl lactate, ethyl lactate, propyl lactate,butyl lactate; methyl propionate, ethyl propionate, benzyl propionate,ethylene carbonate, propylene carbonate, amyl acetate, ethyl benzoate,butyl benzoate, butyl laurate, isopropyl myristate, isopropyl palmirate,triethyl phosphate, tributyl phosphate, diethyl phthalate, dibutylphthalate, diethyl malonate, dipropyl malonate, diethyl succinate,dibutyl succinate, diethyl glutarate, diethyl adipate, dibutyl adipateand diethyl sebacate.

Examples of suitable ethers include butyl phenyl ether, benzyl ethylether, hexyl ether, diethyl ether, dipropyl ether, tetrahydrofuran anddioxane.

Examples of suitable glycols and polyglycols include ethylene glycol,diethylene glycol, triethylene glycol, propylene glycol, dipropyleneglycol and tripropylene glycol.

Examples of suitable glycol and polyglycol derivatives include etherssuch as alkylene glycol mono alkyl ethers, alkylene glycol dialkylethers, polyalkylene glycol monoalkyl ethers, polyalkylene glycoldialkyl ethers and esters of the preceding glycol ethers such as acetateand propionate esters, in case of dialkyl ethers only one ether function(resulting in mixed ether/ester) or both ether functions can beesterized (resulting in dialkyl ester).

Examples of suitable alkylene glycol mono alkyl ethers include ethyleneglycol mono methyl ether, ethylene glycol mono ethyl ether, ethyleneglycol mono propyl ether, ethylene glycol mono butyl ether, ethyleneglycol mono hexyl ether, ethylene glycol mono 2-ethyl-hexyl ether,ethylene glycol mono phenyl ether, propylene glycol mono methyl ether,propylene glycol mono ethyl ether, propylene glycol mono n-propyl ether,propylene glycol mono n-butyl ether, propylene glycol mono iso-butylether, propylene glycol mono t-butyl ether and propylene glycol monophenyl ether.

Examples of suitable alkylene glycol dialkyl ethers include ethyleneglycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycolmethyl ethyl ether, ethylene glycol dibutyl ether, propylene glycoldimethyl ether, propylene glycol diethyl ether and propylene glycoldibutyl ether.

Examples of suitable polyalkylene glycol mono alkyl ethers includediethylene glycol mono methyl ether, diethylene glycol mono ethyl ether,diethylene glycol mono-n-propyl ether, diethylene glycol mono n-butylether, diethylene glycol mono hexyl ether, triethylene glycol monomethyl ether, triethylene mono ethyl ether, triethylene glycol monobutyl ether, dipropylene mono methyl ether, dipropylene glycol monoethyl ether, dipropylene glycol n-propyl ether, dipropylene glycol monon-butyl ether, dipropylene mono t-butyl ether, tripropylene glycol monomethyl ether, tripropylene glycol mono ethyl ether, tripropylene glycolmono n-propyl ether and tripropylene glycol mono n-butyl ether.

Examples of suitable polyalkylene glycol dialkyl ethers includediethylene glycol dimethyl ether, triethylene glycol dimethyl ether,tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether,triethylene glycol diethyl ether, tetraethylene glycol diethyl ether,diethylene glycol methyl ethyl ether, triethylene glycol methyl ethylether, tetraethylene glycol methyl ethyl ether, diethylene glycoldi-n-propyl ether, diethylene glycol di-iso-propyl ether, dipropyleneglycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene din-propyl ether, dipropylene di t-butyl ether, tripropylene glycoldimethyl ether and tripropylene glycol diethyl ether.

Examples of suitable glycol esters include ethylene glycol monomethylether acetate, ethylene glycol monoethyl ether acetate, ethylene glycolmonopropyl ether acetate, ethylene glycol monobutyl ether acetate,diethylene glycol monoethyl ether acetate, diethylene glycol monobutylether acetate, propylene glycol monomethyl ether acetate, propyleneglycol monoethyl ether acetate, dipropylene glycol monomethyl etheracetate and propylene glycol monomethyl ether propionate.

Preferred solvents for use in the pigment dispersion and inkjet inksaccording to the present invention are one or more polyalkyleneglycoldialkylethers represented by the formula (PAG)

wherein R₁ and R₂ are each independently selected from an alkyl grouphaving 1 to 4 carbon atoms;

Y represents an ethylene group and/or a propylene group; wherein n is aninteger selected from 4 to 20 for a first polyalkyleneglycoldialkylether; and n is an integer selected from 5 to 20 for a secondpolyalkyleneglycol.

The alkyl groups R₁ and R₂ of the polyalkyleneglycol dialkylethersaccording to Formula (PAG) preferably represent methyl and/or ethyl.Most preferably, the alkyl groups R₁ and R₂ are both methyl groups.

In a preferred embodiment, the polyalkyleneglycol dialkylethersaccording to Formula (PAG) are polyethylene glycol dialkylethers.

In another preferred embodiment, a mixture of 2, 3, 4 or morepolyalkyleneglycol dialkylethers, more preferably polyethylene glycoldialkylethers are present in the pigment dispersion or inkjet ink.

Suitable mixtures of polyalkyleneglycol dialkylethers for the pigmentdispersions include mixtures of polyethylene glycol dimethyl ethershaving a molecular weight of at least 200, such as Polyglycol DME ₂₀₀™,Polyglycol DME 250™ and Polyglycol DME 500™ from CLARIANT. Thepolyalkyleneglycol dialkylethers used in non-aqueous inkjet inkspreferably have an average molecular weight between 200 and 800, andmore preferably no polyalkyleneglycol dialkylethers with a molecularweight of more than 800 are present. The mixture of polyalkyleneglycoldialkylethers is preferably a homogeneous liquid mixture at roomtemperature.

Suitable commercial glycol ether solvents include Cellosolve™ solventsand Carbitol™ solvents from UNION CARBIDE, Ektasolve™ solvents fromEASTMAN, Dowanol™ solvents from DOW, Oxitoll™ solvents, Dioxitoll™solvents, Proxitoll™ solvents and Diproxitoll™ solvents from SHELLCHEMICAL and Arcosolv™ solvents from LYONDELL.

Lactones are compounds having a ring structure formed by ester bonds andcan be of the γ-lactone (5-membered ring structure), δ-lactone(6-membered ring structure) or ε-lactone (7-membered ring structure)types. Suitable examples of lactones include γ-butyrolactone,γ-valerolactone, γ-hexalactone, γ-heptalactone, γ-octalactone,γ-nonalactone, γ-decalactone, γ-undecalactone, δ-valerolactone,δ-hexalactone, δ-heptalactone, δ-octalactone, δ-nonalactone,δ-decalactone, δ-undecalactone and ε-caprolactone.

Suitable examples of N-containing organic solvents include2-pyrrolidone, N-methylpyrrolidone, N,N-dimethylacetamid,N,N-dimethylformamid, acetonitril and N,N-dimethyldodecanamide.

In another preferred embodiment, the dispersion medium includes oiltypes of liquids, alone or in combination with organic solvent(s).Suitable organic solvents include alcohols, ketones, esters, ethers,glycols and polyglycols and derivatives thereof, lactones, N-containingsolvents such as amides, higher fatty acid ester and mixtures of one ormore of the solvents as described above for solvent based dispersionmedia.

The amount of polar solvent is preferably lower than the amount of oil.The organic solvent preferably has a high boiling point, preferablyabove 200° C. Examples of suitable combinations are disclosed by EP0808347 A (XAAR) especially for the use of oleyl alcohol and EP 1157070A (MARCONI DATA SYSTEMS) for the combination of oil and volatile organicsolvent.

Suitable oils include saturated hydrocarbons and unsaturatedhydrocarbons, aromatic oils, paraffinic oils, extracted paraffinic oils,napthenic oils, extracted napthenic oils, hydrotreated light or heavyoils, vegetable oils, white oils, petroleum naphtha oils,halogen-substituted hydrocarbons, silicones and derivatives and mixturesthereof.

Hydrocarbons may be selected from straight chain or branched chainaliphatic hydrocarbons, alicyclic hydrocarbons and aromatichydrocarbons. Examples of hydrocarbons are saturated hydrocarbons suchas n-hexane, isohexane, n-nonane, isononane, dodecane and isododecane;unsaturated hydrocarbons such as 1-hexene, 1-heptene and 1-octene;cyclic saturated hydrocarbons such as cyclohexane, cycloheptane,cyclooctane, cyclodecane and decalin; cyclic unsaturated hydrocarbonssuch as cyclohexene, cycloheptene, cyclooctene,1,3,5,7-cyclooctatetraene; and cyclododecene; and aromatic hydrocarbonssuch as benzene, toluene, xylene, naphthalene, phenanthrene, anthraceneand derivatives thereof. In literature the term paraffinic oil is oftenused. Suitable paraffinic oils can be normal paraffin type (octane andhigher alkanes), isoparaffins (isooctane and higher iso-alkanes) andcycloparaffins (cyclooctane and higher cycloalkanes) and mixtures ofparaffin oils. The term “liquid paraffin” is often used to refer to amixture of mainly including three components of a normal paraffin, anisoparaffin and a monocyclic paraffin, which is obtained by highlyrefining a relatively volatile lubricating oil fraction through asulphuric-acid washing or the like, as described in U.S. Pat. No.6,730,153 (SAKATA INX). Suitable hydrocarbons are also described asde-aromatized petroleum distillates.

Suitable examples of halogenated hydrocarbons include methylenedichloride, chloroform, tetrachloromethane and methyl chloroform. Othersuitable examples of halogen-substituted hydrocarbons includeperfluoro-alkanes, fluorine-based inert liquids and fluorocarboniodides.

Suitable examples of silicone oils include dialkyl polysiloxane (e.g.,hexamethyl disiloxane, tetramethyl disiloxane, octamethyl trisiloxane,hexamethyl trisiloxane, heptamethyl trisiloxane, decamethyltetrasiloxane, trifluoropropyl heptamethyl trisiloxane, diethyltetramethyl disiloxane), cyclic dialkyl polysiloxane (e.g., hexamethylcyclotrisiloxane, octamethyl cyclotetrasiloxane, tetramethylcyclotetrasiloxane, tetra(trifluoropropyl)tetramethylcyclotetrasiloxane), and methylphenyl silicone oil.

White oil is a term used for white mineral oils, which are highlyrefined mineral oils that consist of saturated aliphatic and alicyclicnon-polar hydrocarbons. White oils are hydrophobic, colorless,tasteless, odourless, and do not change color over time.

Vegetable oils include semi-drying oils such as soybean oil, cotton seedoil, sunflower oil, rape seed oil, mustard oil, sesame oil and corn oil;non-drying oils such as olive oil, peanut oil and tsubaki oil; anddrying oils such as linseed oil and safflower oil, wherein thesevegetable oils can be used alone or as a mixture thereof.

Examples of other suitable oils include petroleum oils, non-drying oilsand semi-drying oils.

Commercially available suitable oils include the aliphatic hydrocarbonstypes such as the Isopar™ range (isoparaffins) and Varsol/Naphtha rangefrom EXXON CHEMICAL, the Soltrol™ range and hydrocarbons from CHEVRONPHILLIPS CHEMICAL, and the Shellsol™ range from SHELL CHEMICALS.

Suitable commercial normal paraffins include the Norpar™ range fromEXXON MOBIL CHEMICAL.

Suitable commercial napthenic hydrocarbons include the Nappar™ rangefrom EXXON MOBIL CHEMICAL.

Suitable commercial de-aromatized petroleum distillates include theExxsol™ D types from EXXON MOBIL CHEMICAL

Suitable commercial fluoro-substituted hydrocarbons includefluorocarbons from DAIKIN INDUSTRIES LTD, Chemical Division.

Suitable commercial silicone oils include the silicone fluid ranges fromSHIN-ETSU CHEMICAL, Silicone Division.

Suitable commercial white oils include Witco™ white oils from CROMPTONCORPORATION.

If the non-aqueous pigment dispersion is a curable pigment dispersion,the dispersion medium includes one or more monomers and/or oligomers toobtain a liquid dispersion medium. Sometimes, it can be advantageous toadd a small amount of an organic solvent to improve the dissolution ofthe dispersant. The content of organic solvent should be lower than 20wt % based on the total weight of the inkjet ink. In other cases, it canbe advantageous to add a small amount of water, for example, to improvethe spreading of the inkjet ink on a hydrophilic surface, but preferablythe inkjet ink contains no water.

Preferred organic solvents include alcohols, aromatic hydrocarbons,ketones, esters, aliphatic hydrocarbons, higher fatty acids, carbitols,cellosolves, higher fatty acid esters. Suitable alcohols includemethanol, ethanol, propanol and 1-butanol, 1-pentanol, 2-butanol,t.-butanol. Suitable aromatic hydrocarbons include toluene, and xylene.Suitable ketones include methyl ethyl ketone, methyl isobutyl ketone,2,4-pentanedione and hexafluoroacetone. Also glycol, glycolethers,N-methylpyrrolidone, N,N-dimethylacetamid, N,N-dimethylformamid may beused.

In the case of a curable inkjet ink, the dispersion medium preferablyincludes monomers and/or oligomers.

Monomers and Oligomers

Any monomer or oligomer may be used as curable compound for the curableinkjet ink. A combination of monomers, oligomers and/or prepolymers mayalso be used. The monomers, oligomers and/or prepolymers may possessdifferent degrees of functionality, and a mixture including combinationsof mono-, di-, tri-and higher functionality monomers, oligomers and/orprepolymers may be used. The viscosity of the inkjet ink can be adjustedby varying the ratio between the monomers and oligomers.

Any method of conventional radical polymerization, photo-curing systemusing photo acid or photo base generator, or photo induction alternatingcopolymerization may be employed. In general, radical polymerization andcationic polymerization are preferred, and photo induction alternatingcopolymerization needing no initiator may also be employed. Furthermore,a hybrid system of combinations of these systems is also effective.

Cationic polymerization is superior in effectiveness due to lack ofinhibition of the polymerization by oxygen, however it is expensive andslow, especially under conditions of high relative humidity. If cationicpolymerization is used, it is preferred to use an epoxy compoundtogether with an oxetane compound to increase the rate ofpolymerization. Radical polymerization is the preferred polymerizationprocess.

Any polymerizable compound commonly known in the art may be employed.Particularly preferred for use as a radiation curable compound in theradiation curable inkjet ink are monofunctional and/or polyfunctionalacrylate monomers, oligomers or prepolymers, such as isoamyl acrylate,stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate,isoamylstyl acrylate, isostearyl acrylate, 2-ethylhexyl-diglycolacrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethylhexahydrophthalicacid, butoxyethyl acrylate, ethoxydiethylene glycol acrylate,methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate,methoxypropylene glycol acrylate, phenoxyethyl acrylate,tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethylacrylate, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate,vinyl ether acrylate, vinyl ether ethoxy (meth)acrylate,2-acryloyloxyethylsuccinic acid, 2-acryloyxyethylphthalic acid,2-acryloxyethyl-2-hydroxyethylphthalic acid, lactone modified flexibleacrylate, and t-butylcyclohexyl acrylate, triethylene glycol diacrylate,tetraethylene glycol diacrylate, polyethylene glycol diacrylate,dipropylene glycol diacrylate, tripropylene glycol diacrylate,polypropylene glycol diacrylate, 1,4-butanediol diacrylate,1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycoldiacrylate, dimethylol-tricyclodecane diacrylate, bisphenol A EO(ethylene oxide) adduct diacrylate, bisphenol A PO (propylene oxide)adduct diacrylate, hydroxypivalate neopentyl glycol diacrylate,propoxylated neopentyl glycol diacrylate, alkoxylateddimethyloltricyclodecane diacrylate and polytetramethylene glycoldiacrylate, trimethylolpropane triacrylate, EO modifiedtrimethylolpropane triacrylate, tri (propylene glycol) triacrylate,caprolactone modified trimethylolpropane triacrylate, pentaerythritoltriacrylate, pentaerithritol tetraacrylate, pentaerythritolethoxytetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropanetetraacrylate, glycerinpropoxy triacrylate, and caprolactam modifieddipentaerythritol hexaacrylate, or an N-vinylamide such as,N-vinylcaprolactam or N-vinylformamide ; or acrylamide or a substitutedacrylamide, such as acryloylmorpholine.

Other suitable monofunctional acrylates include caprolactone acrylate,cyclic trimethylolpropane formal acrylate, ethoxylated nonyl phenolacrylate, isodecyl acrylate, isooctyl acrylate, octyldecyl acrylate,alkoxylated phenol acrylate, tridecyl acrylate and alkoxylatedcyclohexanone dimethanol diacrylate.

Other suitable difunctional acrylates include alkoxylated cyclohexanonedimethanol diacrylate, alkoxylated hexanediol diacrylate, dioxane glycoldiacrylate, dioxane glycol diacrylate, cyclohexanone dimethanoldiacrylate, diethylene glycol diacrylate and neopentyl glycoldiacrylate.

Other suitable trifunctional acrylates include propoxylated glycerinetriacrylate and propoxylated trimethylolpropane triacrylate.

Other higher functional acrylates include ditrimethylolpropanetetraacrylate, dipentaerythritol pentaacrylate, ethoxylatedpentaerythritol tetraacrylate, methoxylated glycol acrylates andacrylate esters.

Furthermore, methacrylates corresponding to the above-mentionedacrylates may be used with these acrylates. Of the methacrylates,methoxypolyethylene glycol methacrylate, methoxytriethylene glycolmethacrylate, hydroxyethyl methacrylate, phenoxyethyl methacrylate,cyclohexyl methacrylate, tetraethylene glycol dimethacrylate, andpolyethylene glycol dimethacrylate are preferred due to their relativelyhigh sensitivity and higher adhesion to an ink-receiver surface.

Furthermore, the inkjet inks may also contain polymerizable oligomers.Examples of these polymerizable oligomers include epoxy acrylates,aliphatic urethane acrylates, aromatic urethane acrylates, polyesteracrylates, and straight-chained acrylic oligomers.

Suitable examples of styrene compounds are styrene, p-methylstyrene,p-methoxystyrene, β-methylstyrene, p-methyl-β-methylstyrene,α-methylstyrene and p-methoxy-β-methylstyrene.

Suitable examples of vinylnaphthalene compounds are 1-vinylnaphthalene,α-methyl-1-vinylnaphthalene, β-methyl-1-vinylnaphthalene,4-methyl-1-vinylnaphthalene and 4-methoxy-1-vinylnaphthalene.

Suitable examples of N-vinyl heterocyclic compounds areN-vinylcarbazole, N-vinylpyrrolidone, N-vinylindole, N-vinylpyrrole,N-vinylphenothiazine, N-vinylacetoanilide, N-vinylethylacetoamide,N-vinylsuccinimide, N-vinylphthalimide, N-vinylcaprolactam andN-vinylimidazole.

The cationically polymerizable compound of the inkjet ink can be one ormore monomers, one or more oligomers or a combination thereof.

Suitable examples of cationically curable compounds can be found inAdvances in Polymer Science, 62, pages 1 to 47 (1984) by J. V. Crivello.

The cationic curable compound may contain at least one olefin,thioether, acetal, thioxane, thietane, aziridine, N-, O-, S- orP-heterocycle, aldehyde, lactam or cyclic ester group.

Examples of cationic polymerizable compounds include monomers and/oroligomers epoxides, vinyl ethers, styrenes, oxetanes, oxazolines,vinylnaphthalenes, N-vinyl heterocyclic compounds, tetrahydrofurfurylcompounds.

The cationically polymerizable monomer can be mono-, di- ormulti-functional or a mixture thereof.

Suitable cationic curable compounds having at least one epoxy group arelisted in the “Handbook of Epoxy Resins” by Lee and Neville, McGraw HillBook Company, New York (1967) and in “Epoxy Resin Technology” by P. F.Bruins, John Wiley and Sons New York (1968).

Examples of cationic curable compounds having at least one epoxy groupinclude 1,4-butanediol diglycidyl ether,3-(bis(glycidyloxymethyl)methoxy)-1,2-propane diol, limonene oxide,2-biphenyl glycidyl ether,3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate,epichlorohydrin-bisphenol S based epoxides, epoxidized styrenics andmore epichlorohydrin-bisphenol F and A based epoxides and epoxidizednovolaks.

Suitable epoxy compounds including at least two epoxy groups in themolecule are alicyclic polyepoxide, polyglycidyl ester of polybasicacid, polyglycidyl ether of polyol, polyglycidyl ether ofpolyoxyalkylene glycol, polyglycidyl ester of aromatic polyol,polyglycidyl ether of aromatic polyol, urethane polyepoxy compound, andpolyepoxy polybutadiene.

Examples of cycloaliphatic bisepoxides include copolymers of epoxidesand hydroxyl components such as glycols, polyols, or vinyl ether, suchas 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexylcarboxylate; bis(3,4-epoxycylohexylmethyl) adipate; limonene bisepoxide; diglycidylester of hexahydrophthalic acid.

Examples of vinyl ethers having at least one vinyl ether group includeethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecylvinyl ether, cyclohexyl vinyl ether, butanediol divinyl ether, hydroxylbutyl vinyl ether, cyclohexane dimethanol monovinyl ether, phenyl vinylether, p-methylphenyl vinyl ether, p-methoxyphenyl vinyl ether,α-methylphenyl vinyl ether, β-methylisobutyl vinyl ether andβ-chloroisobutyl vinyl ether, diethyleneglycol divinyl ether,triethylene glycol divinyl ether, n-propyl vinyl ether, isopropyl vinylether, dodecyl vinyl ether, diethylene glycol monovinyl ether,cyclohexanedimethanol divinyl ether, 4-(vinyloxy)butyl benzoate,bis[4-(vinyl oxy)butyl]adipate, bis[4-(vinyl oxy)butyl]succinate,4-(vinyloxy methyl)cyclohexylmethyl benzoate,bis[4-(vinyloxy)butyl]isophthalate,bis[4-(vinyloxymethyl)cyclohexylmethyl]glutarate,tris[4-(vinyloxy)butyl]trimellitate, 4-(vinyloxy)butyl steatite,bis[4-(vinyloxy)butyl]hexanediylbiscarbamate,bis[4-(vinyloxy)methyl]cyclohexyl]methyl]terephthalate,bis[4-(vinyloxy)methyl]cyclohexyl]methyl]isophthalate,bis[4-(vinyloxy)butyl](4-methyl-1,3-phenylene)-biscarbamate,bis[4-vinyloxy)butyl](methylenedi-4,1-phenylene) biscarbamate and3-amino-1-propanol vinyl ether.

Suitable examples of oxetane compounds having at least one oxetane groupinclude 3-ethyl-3-hydroloxymethyl-1-oxetane, the oligomeric mixture1,4-bis [3-ethyl-3-oxetanyl methoxy)methyl]benzene,3-ethyl-3-phenoxymethyl-oxetane, bis ([1-ethyl(3-oxetanil)]methyl)ether, 3-ethyl-3-[(2-ethylhexyloxy) methyl]oxetane,3-ethyl-[(tri-ethoxysilyl propoxy)methyl]oxetane and3,3-dimethyl-2(p-methoxy-phenyl)-oxetane.

A preferred class of monomers and oligomers which can be used in bothradiation and cationically curable compositions are vinyl etheracrylates such as those described in U.S. Pat. No. 6,310,115 (AGFA),incorporated herein by reference. Particularly preferred compounds are2-(2-vinyloxyethoxy)ethyl (meth)acrylate, most preferably the compoundis 2-(2-vinyloxyethoxy)ethyl acrylate.

Initiators

The curable inkjet ink preferably also contains an initiator. Theinitiator typically initiates the polymerization reaction. The initiatorcan be a thermal initiator, but is preferably a photo-initiator. Thephoto-initiator requires less energy to activate than the monomers,oligomers and/or prepolymers to form the polymer. The photo-initiatorsuitable for use in the curable inkjet inks may be a Norrish type Iinitiator, a Norrish type II initiator or a photo-acid generator.

Thermal initiator(s) suitable for use in the curable inkjet ink includetert-amyl peroxybenzoate, 4,4-azobis(4-cyanovaleric acid),1,1′-azobis(cyclohexanecarbonitrile), 2,2′-azobisisobutyronitrile(AIBN), benzoyl peroxide, 2,2-bis(tert-butylperoxy)butane,1,1-bis(tert-butylperoxy)cyclohexane,1,1-bis(tert-butylperoxy)cyclohexane,2,5-bis(tert-butylperoxy)-2,5-dimethylhexane,2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne,bis(1-(tert-butylperoxy)-1-methylethyl)benzene,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butylhydroperoxide, tert-butyl peracetate, tert-butyl peroxide, tert-butylperoxybenzoate, tert-butylperoxy isopropyl carbonate, cumenehydroperoxide, cyclohexanone peroxide, dicumyl peroxide, lauroylperoxide, 2,4-pentanedione peroxide, peracetic acid and potassiumpersulfate.

The photo-initiator or photo-initiator system absorbs light and isresponsible for the production of initiating species, such as freeradicals and cations. Free radicals and cations are high-energy speciesthat induce polymerization of monomers, oligomers and polymers and withpolyfunctional monomers and oligomers thereby also inducingcross-linking.

Irradiation with actinic radiation may be achieved in two steps bychanging wavelength or intensity. In such cases it is preferred to use 2types of photo-initiators together.

A combination of different types of initiators, for example, aphoto-initiator and a thermal initiator can also be used.

A preferred Norrish type I-initiator is selected from the groupconsisting of benzoinethers, benzil ketals, α,α-dialkoxyacetophenones,α-hydroxyalkylphenones, α-aminoalkylphenones, acylphosphine oxides,acylphosphine sulphides, α-haloketones, α-halosulfones andα-halophenylglyoxalates.

A preferred Norrish type II-initiator is selected from the groupconsisting of benzophenones, thioxanthones, 1,2-diketones andanthraquinones. A preferred co-initiator is selected from the groupconsisting of an aliphatic amine, an aromatic amine and a thiol.Tertiary amines, heterocyclic thiols and 4-dialkylamino-benzoic acid areparticularly preferred as co-initiator.

Suitable photo-initiators are disclosed in CRIVELLO, J. V., et al.VOLUME III: Photoinitiators for Free Radical Cationic and AnionicPhotopolymerization, 2nd Edition, edited by BRADLEY, G., London, UK:John Wiley and Sons Ltd, 1998, pp. 287-294.

Specific examples of photo-initiators may include, but are not limitedto, the following compounds or combinations thereof: benzophenone andsubstituted benzophenones, 1-hydroxycyclohexyl phenyl ketone,thioxanthones such as isopropylthioxanthone,2-hydroxy-2-methyl-1-phenylpropan-1-one,2-benzyl-2-dimethylamino-(4-morpholinophenyl) butan-1-one, benzildimethylketal, bis (2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphineoxide, 2,4,6trimethylbenzoyldiphenylphosphine oxide,2-methyl-1-[4-(methylthio) phenyl]-2-morpholinopropan-1-one,2,2-dimethoxy-1, 2-diphenylethan-1-one or5,7-diiodo-3-butoxy-6-fluorone, diphenyliodonium fluoride andtriphenylsulfonium hexafluophosphate.

Suitable commercial photo-initiators include Irgacure™ 184, Irgacure™500, Irgacure™ 907, Irgacure™ 369, Irgacure™ 1700, Irgacure™ 651,Irgacure ™ 819, Irgacure™ 1000, Irgacure™ 1300, Irgacure™ 1870, Darocur™1173, Darocur™ 2959, Darocur™ 4265 and Darocur™ ITX available from CIBASPECIALTY CHEMICALS, Lucerin TPO available from BASF AG, Esacure™ KT046,Esacure™ KIP150, Esacure™ KT37 and Esacure™ EDB available from LAMBERTI,H-Nu™ 470 and H-Nu™ 470X available from SPECTRA GROUP Ltd..

Suitable cationic photo-initiators include compounds, which form aproticacids or Bronstead acids upon exposure to ultraviolet and/or visiblelight sufficient to initiate polymerization. The photo-initiator usedmay be a single compound, a mixture of two or more active compounds, ora combination of two or more different compounds, i.e., co-initiators.Non-limiting examples of suitable cationic photo-initiators arearyldiazonium salts, diaryliodonium salts, triarylsulphonium salts,triarylselenonium salts and the like.

The curable inkjet ink may contain a photo-initiator system containingone or more photo-initiators and one or more sensitizers that transferenergy to the photo-initiator(s). Suitable sensitizers includephotoreducible xanthene, fluorene, benzoxanthene, benzothioxanthene,thiazine, oxazine, coumarin, pyronine, porphyrin, acridine, azo, diazo,cyanine, merocyanine, diarylmethyl, triarylmethyl, anthraquinone,phenylenediamine, benzimidazole, fluorochrome, quinoline, tetrazole,naphthol, benzidine, rhodamine, indigo and/or indanthrene dyes. Theamount of the sensitizer is in general from 0.01 to 15 wt %, preferablyfrom 0.05 to 5 wt %, based in each case on the total weight of thecurable inkjet ink.

In order to increase the photosensitivity further, the curable inkjetink may additionally contain co-initiators. For example, the combinationof titanocenes and trichloromethyl-s-triazines, of titanocenes andketoxime ethers and of acridines and trichloromethyl-s-triazines isknown. A further increase in sensitivity can be achieved by addingdibenzalacetone or amino acid derivatives. The amount of co-initiator orco-initiators is in general from 0.01 to 20 wt %, preferably from 0.05to 10 wt %, based in each case on the total weight of the curable inkjetink.

A preferred initiator system is2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-(7CI,8CI)4,4′-Bi-4H-imidazole corresponding to the chemical formula:

in the presence of a co-initiator such as 2-mercapto benzoxazole.

Another preferred type of initiator is an oxime ester. A suitableexample has as chemical formula:

A preferred amount of initiator is 0.3-50 wt % of the total weight ofthe curable liquid, and more preferably 1-15 wt % of the total weight ofthe curable inkjet ink.

Irradiation with actinic radiation may be achieved in two steps bychanging wavelength or intensity. In such cases it is preferred to use 2types of photo-initiators together.

Inhibitors

The radiation curable inkjet ink may contain a polymerization inhibitor.Suitable polymerization inhibitors include phenol type antioxidants,hindered amine light stabilizers, phosphor type antioxidants,hydroquinone monomethyl ether commonly used in (meth)acrylate monomers,and hydroquinone, t-butylcatechol, pyrogallol may also be used.

Suitable commercial inhibitors are, for example, Sumilizer™ GA-80,Sumilizer™ GM and Sumilizer™ GS produced by Sumitomo Chemical Co. Ltd.;Genorad™ 16, Genorad™ 18 and Genorad™ 20 from Rahn AG; Irgastab™ UV10and Irgastab™ UV22, Tinuvin™ 460 and CGS20 from Ciba SpecialtyChemicals; Floorstab™ UV range (UV-1, UV-2, UV-5 and UV-8) fromKromachem Ltd, Additol™ S range (S100, S110, S120 and S130) from CytecSurface Specialties.

Since excessive addition of these polymerization inhibitors will lowerthe ink sensitivity to curing, it is preferred that the amount capableof preventing polymerization is determined prior to blending. The amountof a polymerization inhibitor is preferably lower than 2 wt % of thetotal ink.

Binders

Non-aqueous inkjet ink compositions preferably include a binder resin.The binder functions as a viscosity controlling agent and also providesfixability relative to the polymeric resin substrate, e.g., a polyvinylchloride substrate, also called vinyl substrate. The binder must beselected to have a good solubility in the solvent(s).

Suitable examples of binder resins include acrylic resins, modifiedacrylic resins, styrene acrylic resins, acrylic copolymers, acrylateresins, aldehyde resins, rosins, rosin esters, modified rosins andmodified rosin resins, acetyl polymers, acetal resins such as polyvinylbutyral, ketone resins, phenolic resins and modified phenolic resins,maleic resins and modified maleic resins, terpene resins, polyesterresins, polyamide resins, polyurethane resins, epoxy resins, vinylresins, vinyl chloride-vinyl acetate copolymer resins, cellulose typeresins such as nitro cellulose, cellulose acetopropionate and celluloseacetate butyrate, and vinyl toluene-α-methylstylene copolymer resin.These binders may be used alone or in a mixture thereof. The binder ispreferably a film-forming thermoplastic resin.

The amount of binder resin in inkjet ink is preferably in the range of0.1 to 30 wt %, more preferably 1 to 20 wt %, most preferably 2 to 10 wt% based on the total weight of the inkjet ink.

Surfactants

The inkjet ink may contain at least one surfactant. The surfactant(s)can be anionic, cationic, non-ionic, or zwitter-ionic and are usuallyadded in a total quantity less than 20 wt % based on the total weight ofthe inkjet ink and particularly in a total less than 10 wt % based onthe total weight of the inkjet ink.

Suitable surfactants include fluorinated surfactants, fatty acid salts,ester salts of a higher alcohol, alkylbenzene sulphonate salts,sulphosuccinate ester salts and phosphate ester salts of a higheralcohol (for example, sodium dodecylbenzenesulphonate and sodiumdioctylsulphosuccinate), ethylene oxide adducts of a higher alcohol,ethylene oxide adducts of an alkylphenol, ethylene oxide adducts of apolyhydric alcohol fatty acid ester, and acetylene glycol and ethyleneoxide adducts thereof (for example, polyoxyethylene nonylphenyl ether,and SURFYNOL™ 104, 104H, 440, 465 and TG available from AIR PRODUCTS &CHEMICALS INC.).

For non-aqueous inkjet inks, preferred surfactants are selected fromfluoro surfactants (such as fluorinated hydrocarbons) and siliconesurfactants. The silicones are typically siloxanes and can bealkoxylated, polyether modified, polyether modified hydroxy functional,amine modified, epoxy modified and other modifications or combinationsthereof. Preferred siloxanes are polymeric, for examplepolydimethylsiloxanes.

In a curable inkjet ink, a fluorinated or silicone compound may be usedas a surfactant, preferably a cross-linkable surfactant is used.Polymerizable monomers having surface-active effects include siliconemodified acrylates, silicone modified methacrylates, acrylatedsiloxanes, polyether modified acrylic modified siloxanes, fluorinatedacrylates, and fluorinated methacrylates. Polymerizable monomers havingsurface-active effects can be mono-, di-, tri- or higher functional(meth)acrylates or mixtures thereof.

Humectants/Penetrants

Suitable humectants include triacetin, N-methyl-2-pyrrolidone, glycerol,urea, thiourea, ethylene urea, alkyl urea, alkyl thiourea, dialkyl ureaand dialkyl thiourea, diols, including ethanediols, propanediols,propanetriols, butanediols, pentanediols, and hexanediols; glycols,including propylene glycol, polypropylene glycol, ethylene glycol,polyethylene glycol, diethylene glycol, tetraethylene glycol, andmixtures and derivatives thereof. Preferred humectants are triethyleneglycol mono butylether, glycerol and 1,2-hexanediol. The humectant ispreferably added to the inkjet ink formulation in an amount of 0.1 to 40wt % of the formulation, more preferably 0.1 to 10 wt % of theformulation, and most preferably approximately 4.0 to 6.0 wt %.

Preparation of a Pigmented Inkjet Ink

The inkjet ink may be prepared by precipitating or milling the pigmentin the dispersion medium in the presence of the dispersant.

Mixing apparatuses may include a pressure kneader, an open kneader, aplanetary mixer, a dissolver, and a Dalton Universal Mixer. Suitablemilling and dispersion apparatuses are a ball mill, a pearl mill, acolloid mill, a high-speed disperser, double rollers, a bead mill, apaint conditioner, and triple rollers. The dispersions may also beprepared using ultrasonic energy.

Many different types of materials may be used as milling media, such asglasses, ceramics, metals, and plastics. In a preferred embodiment, thegrinding media can include particles, preferably substantially sphericalin shape, e.g., beads consisting essentially of a polymeric resin oryttrium stabilized zirconium beads.

In the process of mixing, milling and dispersion, each process ispreferably performed with cooling to prevent build up of heat.

In the process of mixing, milling and dispersion, each process isperformed with cooling to prevent build up of heat, and for radiationcurable inkjet inks as much as possible under light conditions in whichactinic radiation has been substantially excluded.

The inkjet ink may contain more than one pigment, the inkjet ink may beprepared using separate dispersions for each pigment, or alternativelyseveral pigments may be mixed and co-milled in preparing the dispersion.

The dispersion process can be carried out in a continuous, batch orsemi-batch mode.

The preferred amounts and ratios of the ingredients of the mill grindwill vary widely depending upon the specific materials and the intendedapplications. The contents of the milling mixture include the mill grindand the milling media. The mill grind includes pigment, polymericdispersant and a liquid carrier. For inkjet inks, the pigment is usuallypresent in the mill grind at 1 to 50 wt %, excluding the milling media.The weight ratio of pigment over polymeric dispersant is 20:1 to 1:2.

The milling time can vary widely and depends upon the pigment,mechanical means and residence conditions selected, the initial anddesired final particle size, etc. In a preferred embodiment of thepresent invention, pigment dispersions with an average particle size ofless than 100 nm may be prepared.

After milling is completed, the milling media is separated from themilled particulate product (in either a dry or liquid dispersion form)using conventional separation techniques, such as by filtration, sievingthrough a mesh screen, and the like. Often the sieve is built into themill, e.g., for a bead mill. The milled pigment concentrate ispreferably separated from the milling media by filtration.

In general, it is desirable to make the inkjet inks in the form of aconcentrated mill grind, which is subsequently diluted to theappropriate concentration for use in the inkjet printing system. Thistechnique permits preparation of a greater quantity of pigmented inkfrom the equipment. By dilution, the inkjet ink is adjusted to thedesired viscosity, surface tension, color, hue, saturation density, andprint area coverage for the particular application.

Spectral Separation Factor

The spectral separation factor SSF was found to be an excellent measureto characterize a pigmented inkjet ink, as it takes into accountproperties related to light-absorption (e.g., wavelength of maximumabsorbance λ_(max), shape of the absorption spectrum andabsorbance-value at λ_(max)) as well as properties related to thedispersion quality and stability.

A measurement of the absorbance at a higher wavelength gives anindication on the shape of the absorption spectrum. The dispersionquality can be evaluated based on the phenomenon of light scatteringinduced by solid particles in solutions. When measured in transmission,light scattering in pigment inks may be detected as an increasedabsorbance at higher wavelengths than the absorbance peak of the actualpigment. The dispersion stability can be evaluated by comparing the SSFbefore and after a heat treatment of, e.g., a week at 80° C.

The spectral separation factor SSF of the ink is calculated by using thedata of the recorded spectrum of an ink solution or a jetted image on asubstrate and comparing the maximum absorbance to the absorbance at ahigher reference wavelength λ_(ref). The spectral separation factor iscalculated as the ratio of the maximum absorbance A_(max) over theabsorbance A_(ref) at a reference wavelength

${SSF} = \frac{A_{\max}}{A_{ref}}$

The SSF is an excellent tool to design inkjet ink sets with a largecolor gamut. Often inkjet ink sets are now commercialized, wherein thedifferent inks are not sufficiently matched with each other. Forexample, the combined absorption of all inks does not give a completeabsorption over the whole visible spectrum, e.g., “gaps” exist betweenthe absorption spectra of the colorants. Another problem is that one inkmight be absorbing in the range of another ink. The resulting colorgamut of these inkjet ink sets is low or mediocre.

EXAMPLES

Materials

All materials used in the following examples were readily available fromstandard sources such as Aldrich Chemical Co. (Belgium) and Acros(Belgium) unless otherwise specified. DEGDEE is diethylene glycoldiethylether from ACROS. SOLSPERSE™ 32000 is a hyperdispersant fromNOVEON. Potassium tert-butoxide from ACROS.Methyl-4-(bromomethyl)benzoate from ACROS.Diethyl-5-(hydroxymethyl)isophthalate from ALDRICH. Thionylchloride fromACROS. PR122 is the abbreviation for C.I. Pigment Red 122 for Ink JetMagenta™ E02VP2621 from CLARIANT was used. PV19 is the abbreviation forC.I. Pigment Violet 19 for which Hostaperm Red™ E5B02 from CLARIANT wasused. PR202 is the abbreviation for C.I. Pigment Red 202 for whichCINQUASIA MAG RT235D from CIBA SPECIALTY CHEMICALS was used. PO71 is theabbreviation for C.I. Pigment Orange 71 for which Cromophtal™ DPP OrangeTR from Ciba Specialty Chemicals was used. PR170 is an abbreviation ofC.I. Pigment Red 170 for which NOVOPERM RED F6RK from CLARIANT BENELUXNV was used. PR184 is an abbreviation of C.I. Pigment Red 184 for whichPERMANENT DPP/Quinacridone is the abbreviation for a mixed crystal of adiketopyrrolo-pyrrole/quinacridone mixed crystal pigment for whichChromophtal™ Magenta ST from CIBA SPECIALTY CHEMICALS was used. PR254 isthe abbreviation for C.I. Pigment Red 254 for which Irgazin™ DPP Red BTRfrom Ciba Specialty Chemicals was used PR255 is the abbreviation forC.I. Pigment Red 255 for which Irgazin™ DPP SCARLET EK from CibaSpecialty Chemicals was used.

Measurement Methods

1. Measurement of SSF

The spectral separation factor SSF of the ink was calculated by usingthe data of the recorded spectrum of an ink solution and comparing themaximum absorbance to the absorbance at a reference wavelength. Thereference wavelength is dependent on the pigment(s) used:

-   -   if the color ink has a maximum absorbance A_(max) between and        500 nm then the absorbance A_(ref) must be determined at a        reference wavelength of 600 nm,    -   if the color ink has a maximum absorbance A_(max) between and        600 nm then the absorbance A_(ref) must be determined at a        reference wavelength of 650 nm, and    -   if the color ink has a maximum absorbance A_(max) between and        700 nm then the absorbance A_(ref) must be determined at a        reference wavelength of 830 nm.

The absorbance was determined in transmission with a Shimadzu UV-2101 PCdouble beam-spectrophotometer. The ink was diluted with ethyl acetate tohave a pigment concentration of 0.002%. A spectrophotometric measurementof the UV-VIS-NIR absorption spectrum of the diluted ink was performedin transmission-mode with a double beam-spectrophotometer using thesettings of Table 2. Quartz cells with a path length of 10 mm were usedand ethyl acetate was chosen as a blank.

TABLE 2 Mode Absorbance Wavelength range 240-900 nm Slit width 2.0 nmScan interval 1.0 nm Scan speed Fast (1165 nm/min) Detectorphoto-multiplier (UV-VIS)

Efficient pigmented inkjet inks exhibiting a narrow absorption spectrumand a high maximum absorbance have a value for SSF of at least 30.

2. Dispersion Stability

The dispersion stability was evaluated by comparing the SSF before andafter a heat treatment of one week at 80° C. Pigmented inkjet inksexhibiting good dispersion stability have a SSF after heat treatmentstill larger than 30 and a loss in SSF of less than 35%.

3. Average Particle Size

The particle size of pigment particles in pigmented inkjet ink wasdetermined by photon correlation spectroscopy at a wavelength of 633 nmwith a 4 mW HeNe laser on a diluted sample of the pigmented inkjet ink.The particle size analyzer used was a Malvern™ nano-S available fromGoffin-Meyvis.

The sample was prepared by addition of one drop of ink to a cuvetcontaining 1.5 mL ethyl acetate and mixed until a homogenous sample wasobtained. The measured particle size is the average value of 3consecutive measurements consisting of 6 runs of 20 seconds. For goodink jet characteristics (jetting characteristics and print quality) theaverage particle size of the dispersed particles is below 200 nm,preferably about 100 nm. The pigmented inkjet ink is considered to be astable pigment dispersion if the particle size remained below 200 nmafter a heat treatment of 7 days at 80° C.

Example 1

This example illustrates the synthesis of quinacridone derivativesincluding at least one acid group.

Synthesis of Quinacridone Derivative QAD-1

The quinacridone derivative QAD-1 is represented by the formula:

Synthesis of the dispersion synergist QAD-1 was accomplished accordingto the following synthesis scheme:

31.2 g (0.1 mol) of the pigment PV19 in 500 mL dimethylsulfoxide wasdissolved by addition of 22.44 g (0.2 mol) of potassium tert-butoxide.The blue solution was heated to about 70° C. and 22.8 g (0.1 mol) ofmethyl-4-(bromomethyl)benzoate was added. The mixture was cooled to roomtemperature after 2 hours and the compound QA-1 was precipitated,filtered and washed with methanol. The yield was 77%.

Formation of the dispersion synergist QAD-1 was accomplished byhydrolization of QA-1. This reaction took place during a reflux of 46 g(0.1 mol) of compound QA-1 in a mixture of ethanol and 50 mL (0.5 mol)of 29% sodiumhydroxide solution. After 1 hour the mixture was cooleddown, the precipitate was filtered and washed with water. Theprecipitate was mixed in 1000 mL water and the acid form was made by theaddition of 50 mL (0.6 mol) of concentrated hydrochloric acid. Thedispersion synergist QAD-1 was filtered and washed with water andethanol. The yield was 78%.

Synthesis of Quinacridone Derivative QAD-2

The quinacridone derivative QAD-2 is represented by the formula:

Synthesis of the dispersion synergist QAD-2 was accomplished accordingto the following synthesis scheme:

34.0 g (0.1 mol) of dried pigment PR122 in 500 mL dimethylsulfoxide wasdissolved by the addition of 22.44 g (0.2 mol) potassium tert-butoxide.The blue solution was heated to about 70° C. and 27.1 g (0.1 mol) ofcompound QA-2 was added. The alkylation-step was done after 2 hours andthe product was hydrolyzed by the addition of 72.4 g (0.4 mol) sodiummethylate and 200 mL of water. After 1 hour the mixture was cooled toabout 50° C. and the product was precipitated with acetone (about 1000mL). The precipitate was filtered and washed with acetone. The solidproduct was dissolved in 1000 mL of water and the acid form wasprecipitated by the addition of an excess of concentrated hydrochloricacid. The dispersion synergist QAD-2 was filtered and washed withacetone. The yield was 85%.

Synthesis of Quinacridone Derivative QAD-3

The quinacridone derivative QAD-3 is represented by the formula:

Synthesis of the dispersion synergist QAD-3 was accomplished accordingto the following synthesis scheme:

38.1 g (0.1 mol) of dried pigment PR202 in 130 gram dimethylsulfoxidewas dissolved by the addition of 23 g (0.205 mol) potassiumtert-butoxide. The blue-green solution was heated to about 110° C. for 1hour. Then the mixture was cooled till 40° C., and 25.5 g (0.105 mol) ofcompound QA-2 was added. The alkylation-step was done after 4 hours. Theproduct was hydrolyzed by the addition of 400 ml of water and 19.5 gramPotassium hydroxide 86% (0.3 mol) after 4 hours heating at 60° C. Then75 ml concentrated hydrochloric acid (0.9 mol) was added to the mixture.The dispersion synergist QAD-3 was filtered and washed with water. Theyield was 100%.

Synthesis of dimethyl-(5-chloromethyl)isophthalate (QA-2) wasaccomplished according to the following synthesis scheme:

22.4 g (0.1 mol) of dimethyl-(5-hydroxymethyl)isophthalate (QAOH-2) wasdissolved in a mixture of 100 mL of Toluene and 0.2 g dimethylacetamide(catalyst). 15.4 g (0.13 mol) of thionylchloride was added drop wise andthe mixture was stirred during 4 hour at 40° C. After this period, themixture was cooled in an ice bath and 50 mL of methanol was added. Thissolid product QA-2 was filtered and washed with a small volume ofmethanol. The yield was 58%.

Synthesis of dimethyl-(5-hydroxymethyl)isophthalate QAOH-2 wasaccomplished according to the following synthesis scheme:

25.2 g (0.1 mol) of trimethyl 1,3,5 benzenetricarboxylate was dissolvedin 85 mL of methyl acetate at 50° C. 40.5 ml (0.08 mol)lithiumborohydride 2.0 M in THF was added drop wise and the mixture wasstirred during 3 hour at 50° C. After this period 5.3 gram acetic acid(0.088 mol) and 3 mL water were added. The methyl acetate and THF wereevaporated, 50 ml water and 50 ml n-hexane were added. The productQAOH-2 was filtered and washed with a small volume water and n-hexane.The yield was 63%.

Example 2

This example illustrates that non-aqueous inkjet inks of high dispersionquality and stability can be prepared using a quinacridone derivative incombination with a diketopyrrolo pyrrole pigment or a mixed crystalthereof.

Preparation and Evaluation of a Non-aqueous Inkjet Ink Including a DPPPigment

A milling mixture was prepared with 15 wt % PR254 pigment, 15 wt %polymeric dispersant Solsperse™ 39000 and 1.5 wt % of the quinacridonederivative QAD-3 in DEGDEE as dispersion solvent. The milling mixturewas then milled under cooling by a NETZSCH™ LABSTAR1 at a 50% volumefilling with yttrium-stabilized zirconium oxide-beads of 0.4 mm diameter(“high wear resistant zirconia grinding media” from TOSOH Co.) and aresidence time of 45 minutes. The prepared dispersion exhibited aviscosity of 23 mPa·s. The inkjet ink INV-1 was prepared to obtain acomposition as described in Table 3 by adding 65 parts by weight ofDEGDEE to 35 parts by weight of the milling mixture under stirring atroom temperature.

TABLE 3 wt % of component INV-1 PR254 5.00 QAD-3 0.50 Solsperse ™ 5.0039000 DEGDEE 89.50

The inventive inkjet ink INV-1 exhibited an SSF of 40 and an averageparticle size of 119 nm.

Preparation and Evaluation of Non-aqueous Pigment Dispersions Includinga DPP/Quinacridone Pigment

Two concentrated pigment dispersions were prepared in the same manner toobtain a composition as described in Table 4, except that the dispersionsynergist QAD-3 was either present or absent.

TABLE 4 wt % of component COMP-1 INV-2 DPP/Quinacridone 15.00 15.00QAD-3 — 1.50 Solsperse ™ 39000 15.00 15.00 DEGDEE 70.00 68.50

A milling mixture was prepared with 15 wt % PR255 pigment, 15 wt %polymeric dispersant Solsperse™ 39000 and optionally 1.5 wt % of thequinacridone derivative QAD-3 in DEGDEE as dispersion solvent. Themilling mixture was then milled under cooling by a NETZSCH™ LABSTAR1 ata 50% volume filling with yttrium-stabilized zirconium oxide-beads of0.4 mm diameter (“high wear resistant zirconia grinding media” fromTOSOH Co.) and a residence time of 45 minutes.

The comparative non-aqueous pigment dispersions COMP-1 exhibited aviscosity of 3821 mPa·s, while the inventive non-aqueous pigmentdispersions INV-2 exhibited a viscosity of 29 mPa·s.

Example 3

This example illustrates that non-aqueous inkjet inks of high dispersionquality and stability can be prepared using a quinacridone derivative incombination with a diketopyrrolo pyrrole pigment. Other pigments, suchas Naphtol AS pigments, could not be dispersed by the quinacridonederivative.

Preparation and Evaluation of a Non-aqueous Inkjet Inks

All inkjet inks were prepared in the same manner to obtain a compositionas described in Table 5, except that different pigments and dispersionsynergists were used. In the absence of dispersion synergist QAD-3, apigment concentration of 5.00 wt % instead of 4.50 wt % was used.

TABLE 5 Component wt % Pigment 4.50 QAD-3 0.50 Solsperse ™ 32000 5.00DEGDEE 90.00

An ink composition was made by mixing the pigment, the polymericdispersant Solsperse™ 32000, the dispersion synergist and the organicsolvent DEGDEE with a dissolver and subsequently treating this mixturewith a roller mill procedure using yttrium-stabilized zirconiumoxide-beads of 0.4 mm diameter (“high wear resistant zirconia grindingmedia” from TOSOH Co.). A polyethylene flask of 60 mL was filled to halfits volume with grinding beads and 20 mL of the mixture. The flask wasclosed with a lid and put on the roller mill for three days. The speedwas set at 150 rpm. After milling the dispersion was separated from thebeads using a filter cloth.

Using the above method, the comparative inkjet inks COMP-2 to COMP-7 andthe inventive inkjet inks INV-3 and INV-4 were prepared according toTable 6.

Evaluation of Inkjet Inks

The average particle size and the spectral separation factor SSF weredetermined to evaluate the dispersion quality and were determined againafter a heat treatment of 7 days at 80° C. The results are listed inTable 6.

TABLE 6 After No heat 7d/80° C. treatment % increase Particle % Lossparticle Sample Pigment QAD-3 SSF size (nm) in SSF size COMP-2 PR170 No7 666 0% 0% COMP-3 PR184 No 7 1020 0% 0% COMP-4 PR254 No 31 355 41% 13%COMP-5 PO71 No 177 116 76% 164% COMP-6 PR170 Yes 57 215 67% 11% COMP-7PR184 Yes 18 452 0% 0% INV-3 PR254 Yes 104 124 28% 0% INV-4 PO71 Yes 121100 0% 0%

Poor dispersion quality and/or stability was observed for thecomparative inkjet inks COMP-2 to COMP-7 in the absence of thedispersion synergist or using Naphtol AS pigments. On the other hand,the inventive inkjet inks INV-3 and INV-4 exhibited excellent dispersionquality and stability.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A non-aqueous pigment dispersion comprising: a diketopyrrolo-pyrrolepigment, a polymeric dispersant, and a dispersion synergist in adispersion medium; wherein the dispersion synergist is a quinacridonederivative containing at least one acid group or a salt thereof; and thequinacridone derivative is substituted on only one of two nitrogen atomsof the quinacridone basic chromophore structure by at least one acidgroup or a salt thereof.
 2. The non-aqueous pigment dispersion accordingto claim 1, wherein the at least one acid group or a salt thereof isselected from the group consisting of an alkanoic acid group, analicyclic acid group, a heterocyclic acid group, a hetero-aromatic acidgroup, an aromatic acid group, or salts thereof.
 3. The non-aqueouspigment dispersion according to claim 2, wherein the aromatic acid groupor a salt thereof is a benzoic acid group, a phthalic acid group, anisophthalic acid group, a terephthalic acid group, or salts thereof. 4.The non-aqueous pigment dispersion according to claim 1, wherein thesalt of the at least one acid group is an ammonium acid salt group. 5.The non-aqueous pigment dispersion according to claim 4, wherein theammonium acid salt group is a substituted ammonium group selected fromthe group consisting of ⁺N(CH₃)₂(C₁₈H₃₇)₂, ⁺NH(CH₃)₂(C₁₈H₃₇),⁺N(CH₃)₂(C₁₂H₂₅)₂, ⁺NH(CH₃)₂(C₁₂H₂₅), ⁺N(CH₃)₂(C₁₀H₂₁)₂,⁺NH(CH₃)₂(C₁₀H₂₁), ⁺N(CH₃)₂(C₈H₁₇)₂, ⁺NH(CH₃)₂(C₈H₁₇), ⁺NH(C₈H₁₇)₃,⁺NH(C₁₀H₂₁)₃, ⁺NH(C₁₂H₂₅)₃, and ⁺NH(C₁₈H₃₅)₃.
 6. The non-aqueous pigmentdispersion according to claim 1, wherein the at least one acid group ora salt thereof is a group comprising a carboxyl group or a salt thereof.7. The non-aqueous pigment dispersion according to claim 1, wherein thequinacridone derivative is represented by Formula (I):

wherein R¹ and R² are independently selected from the group consistingof hydrogen, a halogen atom, a methyl group, an ethyl group, antert.-butyl group, a phenyl group, and a cyano group.
 8. The non-aqueouspigment dispersion according to claim 7, wherein thediketopyrrolo-pyrrole pigment is selected from the group consisting ofC.I. Pigment Orange 71, C.I. Pigment Orange 73, C.I. Pigment Orange 81,C.I. Pigment Red 254, C.I. Pigment Red 255, C.I. Pigment Red 264, C.I.Pigment Red 270, C.I. Pigment Red 272, and mixed crystals thereof. 9.The non-aqueous pigment dispersion according to claim 1, wherein thenon-aqueous pigment dispersion is a curable inkjet ink or a non-aqueousinkjet ink containing an organic solvent and/or oil.